OT ... Pregnant Women Should Not Eat Canned Tuna

Canned light tuna, long recommended as the safer choice because of its presumably lower mercury content, sometimes harbors at least as much of that potentially harmful heavy metal as white tuna does, our analysis of Food and Drug Administration data has shown. That finding raises new concerns about the safety of canned tuna for pregnant women.

We scrutinized the results of FDA tests posted recently on its Web site and, as expected, found that most cans of light tuna had only a third as much mercury, on average, as white tuna, also known as albacore. But 6 percent of the light-tuna samples contained at least as much of the metal--in some cases more than twice as much--as the average in albacore. One possible reason: Some canned light tuna may contain yellowfin, which tends to have much more mercury than skipjack, the type usually found in cans labeled as light. (But albacore is generally the only species that's labeled.)

The FDA has not warned consumers about those occasionally higher mercury levels because it believes the levels don't pose any significant threat, according to David Acheson, M.D., the chief medical officer at the agency's Center for Food Safety & Applied Nutrition. "If you eat a single can of something that's a little higher than the average, it's not going to do any acute harm," Acheson said when we asked him about fetal safety.

But Consumer Reports' fish-safety experts note that some cans are much higher in mercury than average. And they say there's enough uncertainty about the safety of even brief exposure of the fetus to such higher mercury levels that a more cautious approach is warranted.

To help guide pregnant women and others who wonder whether tuna and other fish are still safe to eat--and if so, how much--here are CR's answers to 10 crucial questions about mercury in fish. Note that all of the following recommendations for weekly or monthly fish consumption assume that no other mercury-containing seafood is eaten during that time.

1
Why should I bother eating fish if there might be risks?

Some fish are safe for everyone (see question 7), and many others can be safely consumed in limited amounts. And seafood is still an important part of a healthful diet. It contains heart-protecting omega-3 fatty acids. It's also a good source of protein and is usually low in saturated fat.

2
What is mercury, and how does it get into tuna and other fish?

Mercury is a heavy metal, naturally present in rocks and soil, that gets into the environment mainly from emissions generated by coal-burning power plants and waste incinerators. Small amounts are also released as soil and rocks break down or during disposal of products that contain mercury, such as fluorescent light bulbs and certain thermometers. Mercury eventually reaches the oceans and rivers, where bacteria convert it to a more toxic form of the metal, which then accumulates in long-lived predatory fish, including tuna. Indeed, consumption of fish is the primary source of mercury in Americans' bodies.

3
Who's at greatest risk from exposure to mercury, and what's the possible harm?

Fetuses and young children appear to face the most risk, because of their small size and the vulnerability of their developing nervous system. Studies of fish-eating populations have linked low-level mercury exposure in pregnant women and young children with subtle impairments in neurological and behavioral functioning, such as hearing, eye-hand coordination, and learning ability. Other evidence suggests that frequent consumption of high-mercury fish by adults may affect the neurologic, cardiovascular, and immune systems.

The effects of sporadic exposure to the higher mercury levels in some light-tuna cans have not been determined. But some scientists are concerned that even brief exposure to those mercury levels at critical points in fetal development may be harmful. For example, studies in primates and rats have shown that mercury blocks the ability of developing brain cells to migrate to the proper place and form appropriate connections. Moreover, our consultants say studies have not established that there's any minimal frequency, duration, or amount of mercury exposure that is safe for the fetus.

4
Should those who are most susceptible to the effects of mercury eat canned tuna?

Based on the FDA data and the mercury- exposure levels that the Environmental Protection Agency deems acceptable, here's what our experts recommend:

Pregnant women. Given the uncertainties about the safety of even chunk-light tuna, we think it's prudent for pregnant women to avoid canned tuna entirely.

Young children (up to about 45 pounds). They can safely eat about one-half to one 6-ounce can (roughly 4.5 ounces drained) of chunk-light tuna per week, or up to one-third of a can of solid-light or white, depending on their weight. The advice about solid-light is based on limited FDA data suggesting that it may contain considerably more mercury, on average, than chunk-light does, though less than albacore.

Women of childbearing age who aren't pregnant. Mercury can linger in the body after you stop eating fish. So we advise these women to eat no more than about three chunk-light cans per week, or one can of solid-light or white-tuna.

5
How much canned tuna can older kids eat?

It's not clear exactly when children become less vulnerable to mercury; indeed, the brain continues to develop through the teenage years. Nevertheless, government regulators assume that the heavier the child, the more mercury can be safely consumed. Our experts think it's prudent for children weighing anywhere from about 45 pounds to 130 pounds to eat no more than one to three cans of chunk-light tuna per week, depending on their weight. Or they could have one-third to one can of solid-light or white tuna per week.

6
What about canned tuna for men and older women?

The same weekly intake that's considered safe for women of childbearing age who are not pregnant--roughly three cans of chunk-light tuna or one can of solid-light or white--is almost surely safe for men and older women as well. They can quite likely eat more than that without harm, but the exact amounts are not known.

7
Are there any types of fish that are low in mercury?

Some seafood species--salmon, shrimp, clams, and tilapia--have such consistently low mercury levels that everyone, including pregnant women and young children, can safely eat them every day. (Choosing wild salmon minimizes exposure to a number of other pollutants.) Other low-mercury species, including oysters, hake, sardines, crawfish, pollock, herring, flounder, sole, mullet, Atlantic mackerel, scallops, crab, and Atlantic croaker, can be consumed anywhere from once a week to daily, depending on body weight and the fish species (see Low-mercury seafood choices).

8
What about all the other fish--should I restrict my intake of those, too?

Fish other than the low-mercury types listed above should be eaten in more limited amounts or not at all, as follows:

Pregnant women. Follow the FDA recommendation and don't eat tilefish, shark, swordfish, or king mackerel, which are very high in mercury. We further suggest that pregnant women limit their seafood choices to the low-mercury species listed under question 6, for two reasons. Some species--including Chilean bass, halibut, American lobster, and Spanish mackerel--occasionally contain as much mercury as the most contaminated types, such as swordfish. And some fish have not been thoroughly tested for mercury.

Women of childbearing age and all children. They should avoid the same four high-mercury fish that are off-limits to pregnant women. As for other fish, apart from those on our low-mercury list, the amount of the metal they contain varies greatly. Some fish can be safely consumed only once a month, while others can be eaten many times. People who want to be as safe as possible can minimize their consumption of these fish.

Women beyond childbearing age and men. More frequent fish intake, including a very occasional serving of a high-mercury species, is unlikely to cause harm. But studies have not determined the acceptable amounts. To be on the safe side, those people may want to follow the advice for women of childbearing age.

Note that state agencies and the Environmental Protection Agency periodically issue advisories for locally caught fish based on regional contaminant levels. To find advisories for your region, go to www.epa.gov/waterscience/fish/states.htm .

9
Is there a way to get the benefits of fish without actually eating it?

Fish-oil supplements appear to be a safe, reliable way to get omega-3 fatty acids. When we last tested those pills, for our July 2003 report, we found no problems with quality or with worrisome amounts of any of the heavy metals we assessed, including mercury. But women of childbearing age and young children's parents should still check with their doctor before taking those pills or giving them to kids. As for protein, reasonably low-fat sources include skinless white chicken, lean beef or pork, tofu, and beans.

10
Should the government be doing more to protect consumers against mercury in tuna and other fish?

Consumers Union, publisher of Consumer Reports, thinks the FDA should take several steps. First, the agency should strengthen its advice to vulnerable groups about eating fish. In particular, it should make its recommendations on albacore tuna consistent with its advice on other fish by reducing the amounts of albacore it says is safe for those groups to consume. It needs to further revise its warnings to pregnant women to account for the occasional peak mercury levels in tuna and other fish. The FDA also should develop advice for men and older women and conduct more extensive tests, especially of commonly eaten species such as tilapia and clams. In addition, we urge the FDA to require that information about mercury risks be posted on canned-tuna labels and in stores and restaurants that sell or serve fish.